Atomistic Investigations of Occupancy-Driven Structural Deformations in Binary H2-THF Hydrates and Their Effect on Storage Capacity

Hydrogen is a clean fuel with the highest specific energy density and is central to net-zero goals, but its low volumetric energy density creates storage challenges that limit capacity and complicate deployment. Gas hydrates are hydrogen-bonded crystalline solids composed of water molecules forming polyhedral cages that trap gas molecules (guests). Pure hydrogen hydrates can achieve storage capacities comparable to or exceeding conventional systems and U.S. Department of Energy (DOE) targets, but their requirement for extreme pressures and low temperatures limits practical use. Thermodynamic promoters such as tetrahydrofuran (THF) substantially reduce formation pressures but displace hydrogen, therefore reducing capacity. We employ density functional theory (DFT) to examine how guest occupancy affects storage capacity in H2-THF binary hydrates, leveraging atomic-level control not accessible experimentally. We identify a two-step structural response to increasing H2 loading: an initial uniform lattice expansion that accommodates additional guests, followed by heterogeneous deformation that defines the upper occupancy limits. Using these occupancy ceilings, we find that binary hydrates can exceed DOE targets when THF loading is sufficiently low. These atomistic insights clarify the mechanisms underlying occupancy-driven structural behaviour and establish theoretical limits that can guide the design and optimization of hydrate-based hydrogen storage materials.